For the production of record carriers for electroerosion printers, papers are coated with lacquers which in most cases contain the following pigments.
(a) Carbon black as a black pigment with a very large specific surface and a very small primary grain of about 0.05 .mu.m. Therefore, carbon black must always be incorporated as a secondary grain in the lacquer. However, secondary grains have a low mechanical stability, i.e., they are easily smashed, thus leading to enhanced lacquer wear and pronounced abrasion during printing. Being non-polar, this pigment is only moderately compatible with the cellulose esters of the lacquer. Although penetration into to secondary grains enhances the polymer's internal adhesion to carbon black, it leads to an extraordinarily high degree of shrinkage of the lacquer film during curing.
(b) Black iron oxides are very hard and lead to a very high wear of the electrodes. These pigments form crystals with an atomic lattice structure, which are marked by great hardness and moderate polarity, thus being well compatible with the cellulose acetobutyrate of the lacquer.
(c) The characteristics of the white pigments, such as diatomaceous earth, quartz, and titanium dioxide, are identical with those mentioned under (b), with titanium dioxide having an extraordinarily high covering power, so that redying the lacquer black is difficult.
(d) According to a previous proposal, calcium carbonate was used as a dulling agent and particularly as a means for preventing an undesirable baking at the electrodes. This pigment does not lead to an irregular wear of the electrodes, which has been found to be a serious disadvantage with the pigments under (b) and (c).
CaCO.sub.3 has an ion lattice crystal structure and thus a much greater polarity than cellulose acetobutyrate. Although the free --OH-groups in the cellulose acetobutyrate make for a certain degree of compatibility with CaCO.sub.3, the surface tension of the solvent and the cellulose acetobutyrate relative to CaCO.sub.3 is so high that the calcium carbonate grains on the surface of the lacquer have relatively sharp contours. This is due to the fact that the calcium carbonate grains are covered with a thin layer of cellulose acetobutyrate. As a result, the lacquer film has a low internal cohesion and its oil absorption is much too low. An improvement could be achieved by using a commercially available CaCO.sub.3 coated with stearic acid.
(e) Finally, there are high-polymer granulated materials with a grain size distribution in the .mu.m range. However, it is unknown how such materials behave, but it is necessary for such pigments to be well compatible with the polymers of the lacquer and to be totally insoluble in the solvents used, in order to prevent the formation of mixed polymers.